1,720,985 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Mechanistic and functional studies of the interaction of a proline-rich antimicrobial peptide with mammalian cells
No full textRanacyclins, a new family of short cyclic antimicrobial peptides: biological function, mode of action, and parameters involved in target specificity
No full textWe report on two new cyclic 17-residue peptides that we named ranacyclins E and T, the first isolated from Rana esculenta frog skin secretions and the second discovered by screening a cDNA library from Rana temporaria. Ranacyclins have a loop region that is homologous with that of an 18-mer peptide, pLR, isolated from the skin of the Northern Leopard frog, Rana pipiens, with no reported antimicrobial
activity. Here we show that ranacyclins and pLR have antimicrobial and antifungal activity. However,
despite the high structural similarity, they differ in their spectrum of activity. The data reveal that ranacyclins
and pLR have several properties that differentiate them from most known antimicrobial peptides. These
include the following: (i) they adopt a significant portion of random coil structure in the membrane as
revealed by ATR-FTIR and CD spectroscopy (50% for ranacyclin T and 70% for both ranacyclin E and
pLR); (ii) they bind similarly to both zwitterionic and negatively charged membranes as revealed by
using tryptophan fluorescence and surface plasmon resonance (SPR; BIAcore biosensor); (iii) they insert
into the hydrophobic core of the membrane and presumably form transmembrane pores without damage
to the bacterial wall, as revealed by SPR, ATR-FTIR, and transmission electron microscopy (TEM); and
(iv) despite being highly and equally active in permeating bacterial spheroplasts and negatively charged
membranes, they differ significantly in their potencies against target cells. Furthermore, a significant fraction
of a given secondary structure is not prerequisite for membrane permeation and antimicrobial activity.
However, increasing the fraction of a secondary structure and reducing peptide assembly in the membrane
make it easier for the peptide to diffuse through the cell wall, which is different for each microorganism,
into the cytoplasmic membrane
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Effect of natural L- to D-amino acid conversion on the organization, membrane binding, and biological function of the antimicrobial peptides bombinins H.
No full textAntimicrobial peptides (AMPs) are evolutionarily old components of innate immunity found in all living pluricellular organisms. Interestingly, some organisms express families of AMPs with only a slight variation among their members, possibly to increase their spectrum of activity. Despite the growing body of knowledge about their biological activity and mode of action on bacteria, only a few of them have been tested on Leishmania, a worldwide spread protozoan pathogen, and the parameters contributing to this activity are yet to be determined. We report on the anti-Leishmania activity and mode of action of bombinins H2 and H4 isolated from the skin secretion of the frog Bombina variegata. H4, the most active, is the first natural AMP of animal origin with a single L- to D-amino acid isomerization. Membrane depolarization and membrane permeation assays, as well as electron microscopy, suggest that the lethal mechanism involves plasma membrane permeation and/or disruption. To better understand the enhanced activity of H4, we determined the peptide's structure in membranes mimicking those of mammals, bacteria, and Leishmania by using ATR-FTIR and CD spectroscopies and assessed their membrane binding by using surface plasmon resonance. The data reveal that (i) H2 but not H4 partially aggregates in membranes mimicking those of Leishmania, (ii) H2 is slightly more helical than H4 in all membranes, and (iii) H4 binds the Leishmania model membrane approximately 5-fold better than H2. This study highlights the importance of a single alpha-amino acid epimerization as a tool used by nature to modulate the activity of AMPs. In addition, our findings suggest bombinins H as potential templates for the development of new drugs with a new mode of action against Leishmania
Controlled alteration of the shape and conformational stability of alpha-helical cell-lytic peptides: effect on mode of action and cell specificity
No full textA novel method, based on the rational and systematic modulation
of macroscopic structural characteristics on a template originating
from a large number of natural, cell-lytic, amphipathic α-helical
peptides, was used to probe how the depths and shapes of hydrophobic
and polar faces and the conformational stability affect
antimicrobial activity and selectivity with respect to eukaryotic
cells. A plausible mode of action explaining the peptides’ behaviour
in model membranes, bacteria and host cells is proposed.
Cytotoxic activity, in general, correlated strongly with the hydrophobic
sector depth, and required a majority of aliphatic residue
side chains having more than two carbon atoms. It also correlated
significantly with the size of polar sector residues, which determines
the penetration depth of the peptide via the so-called
snorkel effect. Both an oblique gradient of long to short aliphatic
residues along the hydrophobic face and a stabilized helical
structure increased activity against host cells but not against bacteria,
as revealed by haemolysis, flow cytofluorimetric studies on
lymphocytes and surface plasmon resonance studies with model
phosphatidylcholine/cholesterol membranes. The mode of interaction
changes radically for a peptide with a stable, preformed
helical conformation compared with others that form a structure
only on membrane binding. The close correlation between effects
observed in biological andmodel systems suggests that the ‘carpet
model’ correctly represents the type of peptides that are bacteriaselective,
whereas the behaviour of those that lyse host cells is
more complex
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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